Method and apparatus for adaptive control

ABSTRACT

The invention is for a method of self-adaptation of a feedforward type of model incorporated online in a control system supplying &#39;&#39;&#39;&#39;anticipatory&#39;&#39;&#39;&#39; control to a dependent system variable based on the value of an independent system variable. The feedforward model, for example, may employ a proportional and a bias function which together express a linear estimate of the modification of the independent system variable value required to compute a suitable control for the dependent system variable. The invention is for a procedure performed while the system is under control action, employing the steps of monitoring the condition of the independent system variable, or in some cases, the set point, and selecting in accordance therewith one of the feedforward model functions for an adjustment, which adjustment uses the system error signal in a feedback loop type of control action in order to reduce that error. Each such selection, together with the adjustment performed, acts to improve the model&#39;&#39;s estimate of the proper relationship between the value of the independent system variable and the value of the dependent system variable. Over a period of time, as the independent variable changes, several successive selections and adjustments will be made, and the model will express the best possible estimate, whether the model is a simple linear model, or is made to represent a more complex group of functions. The invention also includes apparatus for carrying out the adaptation. Applications are also included where the model is employed in other than the conventional feedforward control situations, the adaptation feature of the invention providing for automatic calibration of measurements, and for on-off control activity, for example.



1. A method for adjusting factors each in one of a plurality of mathematical functions that express an estimate of the relationship between the value of an independent system variable and the required value of a dependent system variable for minimizing a measured error in a system wherein said estimate is employed to compute the regulation of said dependent system variable from the value of said independent system variable comprising the steps of: ascertaining a change in the condition of said independent system variable, selecting in accordance with said change one of said factors for adjusting, and adjusting the value of said selected factor in a manner tending to reduce said measured system error said adjusting thereby tending to optimize said estimate.
 2. The method of claim 1 wherein the step of ascertaining a change in the condition of said independent system variable is based upon discrimination of a change in value of said independent system variable.
 3. The method of claim 1 wherein the step ascertaining a change in the condition of said independent system variable is based upon detection of a predetermined minimum change in said condition so that said change includes a sufficient change in value to insure adjusting the newly selected factor while said system experiences an appreciably new value of the independent variable.
 4. The method of claim 1 wherein the step ascertaining a change in the condition of said independent system variable includes evaluation of the rate and magnitude of said change in condition.
 5. The method of claim 1 wherein the step of adjusting the value of said selected factor employs an integration of system error for adjusting said value of said selected factor.
 6. The method of claim 1 wherein said mathematical functions are terms in a polynomial and the step of selecting a factor for adjusting is performed in accordance with a predetermined rule employing the value of said independent system variable, so that upon the occurrence of a predetermined increase in the value of said independent system variable a selection in accordance with said rule is made of the factor of a term of said polynomial having a larger exponent relative to the exponent of the term of said polynomial that had its factor adjusted previously to said occurrence of said predetermined increase and upon the occurrence of a predetermined decrease in the value of said independent system variable a selection in accordance with said rule is made of the factor of a term of said polynomial having a smaller exponent relative to the exponent of the term of said polynomial that had its factor adjusted previously to said occurrence of said predetermined decrease.
 7. The method of claim 6 wherein a particular factor is selected for adjusting in the step of selecting a factor during times the independent system variable does not minimally change thereby providing a feedback loop during such times based upon said system error operating through said particular factor selected to provide said regulation of said dependent system variable to maintain said system error at a minimum.
 8. A method for adjusting factors each in one of a plurality of terms in a polynomial that express an estimate of the relationship between the value of an independent system variable and the required value of a dependent system variable for minimizing measured error in a system wherein said estimate is employed to compute the regulation of said dependent system variable from the value of said independent system variable comprising the steps of: ascertaining the direction of any change of the value of said independent system variable exceeding a predetermined magnitude, selecting one of said factors for adjusting in accordance with said direction so ascertained so that upon the occurrence of a predetermined increase in the value of said independent system variable a selection is made of the factor of a term of said polynomial having a larger exponent relative to the exponent of the term of said polynomial that had its factor adjusted previously to said occurrence of said increase and upon the occurrence of a predetermined decrease in the value of said independent system variable a selection is made of the factor of a mathematical operation having a smaller exponent relative to the exponent of the mathematical operation that its factor adjusted previously to said occurrence of said decrease, adjusting the value of said selected factor in a manner tending to reduce said measured system error thereby optimizing said selected factor so that said polynomial estimate of said relationship between said variable is improved.
 9. The method of claim 8 incorporating a time delay in the step of selecting so that a time delay is inserted between successive adjustments of alternate factors.
 10. A method for correcting an inaccurate system measurement by reference to an accurate system measurement wherein an estimate of the relationship between said inaccurate system measurement and said accurate system measurement is represented by a model performing a plurality of mathematical operations each operation having an adjustable factor and said model having an input responsive to said inaccurate measurement and having an output representing a correction of said inaccurate measurement comprising the steps of: selecting in accordance with a change in the condition of one of said measurements one of said factors for adjusting, and adjusting the value of said selected factor using the value of the accumulated deviation in said inaccurate measurement from said accurate measurement in a manner tending to reduce said deviation said adjusting thereby optimizing said estimate.
 11. The method of claim 10 wherein the step of selecting in accordance with the condition of a measurement employs said inaccurate system measurement.
 12. The method of claim 10 wherein the step of selecting in accordance with the condition of a measurement employs said accurate system measurement.
 13. A method for adjusting factors one in an additive mathematical operation and one in a multiplicative mathematical operation said operations together expressing a linear estimate of the relationship between the value of an independent system variable and the required value of a dependent system variable for minimizing measured error in a system wherein said linear estimate is employed to compute the regulation of said dependent system variable from the value of said independent system variable comprising the steps or: ascertaining the occurrence of a predetermined change in value of said independent system variable, selecting one of said factors in accordance with the direction of said occurrence so that for an increasing change in value of said iNdependent system variable a selection is made of said multiplicative factor and for a decreasing change in value of said independent system variable a selection is made of said additive factor, integrating said system error, and employing the value of said integrated system error for the adjusted value of said selected factor in a manner tending to reduce said measured system error so that said estimate is improved.
 14. The method of claim 13 wherein one of said factors is selected during times said independent system variable is stable thereby forming a feedback path through the selected factor to said dependent system variable thereby minimizing said measured system error.
 15. An adapting control apparatus for a system having a significant relationship between the value of an independent system variable and the required value of a controlled system variable for minimizing measured system error comprising: a mathematical model estimating said relationship performing an additive operation and a multiplicative operation each operation having an adjustable factor and said mathematical model having an input responsive to the value of said independent system variable and having a computed output for regulating said controlled system variable, a feedback controller having an input responsive to said measured system error and having an output for adjusting said factor of said additive operation, a first band-pass filter having an input responsive to the value of said independent system variable and having an output, a second band-pass filter having an input responsive to the value of said controlled system variable and having an output, means for determining the ratio between the outputs of said first and second band-pass filters and having an output signifying said ratio, an averaging device responsive to said output of said means for determining the ratio having an output for adjusting said factor of said multiplicative operation and having a controllable time constant whereby the time constant of said averaging device may be set to maintain said output of said averaging device at its last level for an indefinite time, and a circuit responsive to said outputs of said first and second band-pass filters and having an output controlling said controllable time constant of said averaging device whereby said time constant is set to maintain said output of said averaging device at its last level for an indefinite time if the absolute value of said output of either said first or second band-pass filters is less than some minimum predetermined value.
 16. An adapting control apparatus for a system having a significant relationship between the value of an independent system variable and the required value of a controlled system variable for minimizing measured system error comprising: a mathematical model estimating said relationship performing a plurality of operations each operations having an adjustable factor and said mathematical model having an input responsive to the value of said independent system variable and having a computed output for regulating said controlled system variable whereby said controlled system variable is regulated according to the relationship estimated by said mathematical model, and a plurality of adjusting means one for each said adjustable factor each adjusting means having an output for adjusting the value of its respective factor and each having an input which is made responsive to a signal representing said system error in accordance with a predetermined rule employing the value of said independent variable thereby forming a feedback path from said system error to said controller variable said path including the one of said adjusting means in accordance with said rule made responsive to a signal representing system error and including the one of said plurality of operations of said model having its factor thereby selected for adjusting by said adjusting means.
 17. An adaptinG control apparatus for a process wherein there exists a determinable relation between the value of an independent process variable and the required value of a controlled process variable for maintaining a process measurement at a process set point comprising: a feedforward model responsive to the value of said independent process variable performing an additive mathematical operation having an adjustable bias factor and performing a multiplicative mathematical operation having an adjustable proportional factor said operations expressing a linear estimate of said relationship and said model having an output for regulating said controlled process variable, means for adjusting said bias factor said means being responsive to a signal representing said process measurement deviation from said process set point upon the occurrence of a predetermined change of the value of said independent process variable in a decreasing direction, means for adjusting said proportional factor being responsive to said signal upon the occurrence of a predetermined change of the value of said independent process variable in an increasing direction, whereby the one of said factors adjusted by the one of said means for adjusting responsive to said signal is thereby included in a feedback loop with said process so that said signal tends to adjust said factor adjusted in a manner to make said output of said model regulate said controlled process variable to bring said process measurement to said process set point and whereby the successive adjusting of said bias factor and said proportional factor serves to make said linear estimate more closely approximate said relationship.
 18. The apparatus of claim 17 wherein one of the factors of said feedforward model is selected for adjusting during times that said independent variable is substantially stable.
 19. The apparatus of claim 16 wherein said mathematical model consists of a polynomial and said predetermined rule is based on a predetermined change of magnitude and direction of said value of said independent variable so that upon the occurrence of a predetermined increase in the value of said independent system variable a selection is made of the factor of a term of said polynomial having a larger exponent relative to the exponent of the term of said polynomial that had its factor adjusted previously to said occurrence of said predetermined increase and upon the occurrence of a predetermined decrease in the value of said independent system variable a selection is made of the factor of a term of said polynomial having a smaller exponent relative to the exponent of the term of said polynomial that had its factor adjusted previously to said occurrence of said predetermined decrease.
 20. The apparatus of claim 17 including means for making said means for adjusting said bias factor responsive to said signal upon the occurrence of a predetermined change of the value of said independent process variable in a decreasing direction and including means for making said means for adjusting said proportional factor responsive to said signal upon the occurrence of a predetermined change of the value of said independent process variable in an increasing direction.
 21. The apparatus of claim 17 including means for providing a time delay between operation of said means for adjusting said bias factor and operation of said means for adjusting said proportional factor whereby alternating operation of said respective means incorporates said time delay between each alternation.
 22. The apparatus of claim 17 wherein a varying set point is substituted for said independent process variable whereby said model is adapted to estimate the relationship between said varying set point and said controlled process variable.
 23. The apparatus of claim 17 wherein said process has a plurality of independent process variables each having a determinable relationship with said controlled process variable for maintaining a process measurement at a process set point, said control apparatus including an additional proportional factor for each additional independent process variable.
 24. The apparatus of claim 23 wherein said bias factor performs the additive mathematical operations for all of the additional independent variables.
 25. The apparatus of claim 23 with logic for deciding the appropriate factor for adjusting when more than one independent variable changes simultaneously.
 26. An adapting control apparatus for a system employing a varying set point wherein a system valve is manipulated to control a system measurement to follow said varying set point comprising: means for setting said valve to one of its two extreme positions in accordance with the direction of a variation in said set point, means for setting said valve to a relatively long term position in accordance with a relatively long term value of said varying set point, a first adjusting means responsive to the instantaneous deviation of said system measurement from said system set point during a first period determined in accordance with a predetermined rule and having an output adjusting the instant for setting said valve to its relatively long term position, and a second adjusting means responsive to the instantaneous deviation of said system measurement from said set point during a second period determined in accordance with said rule and having an output adjusting said valve to its relatively long term position thereby adjusting said manipulation of said valve in a manner to make said system measurement follow closely said varying set point.
 27. The control apparatus of claim 26 in which said varying set point includes step changes.
 28. The adapting control apparatus of claim 26 including a prior adjusting means responsive to the instantaneous deviation of said system measurement from said system set point during a period prior to said first period determined in accordance with said rule and having an output adjusting the instant for setting said valve to one of its two extreme positions.
 29. The adapting control apparatus of claim 26 wherein said rule is based on the value of said system measurement.
 30. The adapting control apparatus of claim 26 wherein said rule is based on the value of said varying set point.
 31. The adapting control apparatus of claim 26 including means for setting said valve to the opposite of said one of its two extreme positions thereby providing for alternation of said valve between the two extreme positions for a predetermined number of times and including adjusting means for adjusting each instant for setting said valve to said opposite position responsive to said deviation during a predetermined period.
 32. A method for adjusting a valve program for making a system measurement follow a variation in system set point comprising the steps of: determining first time for turning a valve full on by reference to the deviation of a system measurement change from a system step change in set point during a first predetermined period, determining the time for positioning said valve to an intermediate position by reference to the deviation of said system measurement from said set point during a second predetermined period, and determining said intermediate position of said valve by reference to the deviation of said system measurement from said set point during a third predetermined period.
 33. Apparatus for adjusting factors, each in one of a plurality of mathematical functions that express an estimate of the value of an independent system variable and the required value of a dependent system variable for minimizing a measured error in a system wherein said estimate is used to compute the regulation of said dependent system variable from the value of said independent system variable, comprising: means for ascertaining a change in the condition of said independent system variable, means for selecting in accordance with said change one of said factors for adjusting, and means fOr adjusting the value of said selected factor in a manner tending to reduce said measured system error, said adjusting thereby tending to optimize said estimate.
 34. The apparatus of claim 33 wherein said independent system variable is a varying set point.
 35. The apparatus of claim 33 wherein said independent system variable is a varying set point and said means for selecting operates in accordance with a change in the value of the measured error.
 36. The method of claim 1 wherein said independent system variable is a varying set point.
 37. The method of claim 1 wherein said independent system variable is a varying set point and said step of selecting is performed in accordance with a change in the value of the measured error. 